This invention is concerned with apparatus for reading a line marking fixed to a carrier, the marking comprising a succession of line-like elements of differing lengths which are arranged substantially parallel to one another, the shorter elements being used as pulse generator markings and the longer elements as code symbols, the apparatus operating in conjunction with an optical apparatus which displays the elements in turn on a reading surface as the marking carrier is moved transversely to the direction in which the elements extend, the reading surface being divided into a plurality of sectors each of which is associated with an optoelectronic transducer which, when illuminated, produces an electrical output signal.
Various types of such apparatus are known for reading markings of various kinds. One of these types is designed for reading line markings, the line-like elements of which are formed in relief on the cylindrical wall or the bottom contraction of a container. The problems involved in reading such line markings and an apparatus which overcomes these problems are described in the specification of European Patent Application No. 0105715. This apparatus comprises an optical arrangement which displays the line-like elements in turn on a reading surface. The reading surface is divided into more than three consecutive sectors and a pulse signal indicating a shorter element is produced whenever an element is displayed on a sector. A pulse signal indicating a longer element is produced whenever an element is displayed simultaneously on at least two sectors which are separated from one another by at least one other sector. When using the appratus described in said specification for reading the mould number in which glass or plastics containers have been moulded, each element of the marking has to be read within a time of less than 0.2 milliseconds. This is especially difficult if the individual elements are off-set relative to one another in their longitudinal direction, if their surface is imperfectly shaped, or if the container does not assume a vertical position in the rotating apparatus so that the marking is inclined to the reading plane.
The object of the present invention is to improve the apparatus described in the aforementioned patent specification to increase its accuracy.